The 200-400mm f/4L offers lightening-quick, smooth, and incredibly accurate auto-focus capabilities for Canon EOS cameras. The lens focuses so fast and so effortlessly, that you literally cannot see it happening in the viewfinder

The lens is “pretty damned sharp – both with the extender and without” and “is impervious to almost any weather Mother Nature can throw at you“. From the conclusion:

Is the lens “worth” it? Who the hell knows? It will be worth it to some photographers and certainly not worth it to others. As a professional nature and wildlife photographer, it’s the lens I’ve waiting on for a long time. It’s the ultimate wildlife lens, period. But I already knew that two years ago before I ever got my hands on it. The only question was whether Canon delivered a clunker or hit a home run with the finished product. It appears to be the latter.

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